A convenient method for testing the operation and accuracy of commercial pulse oximeters does not yet exist. Our work has been directed toward the development of a calibrator that employs a liquid-crystal light valve to simulate the optical signals measured by pulse oximeters. Last year we completed a prototype instrument based on a custom-made liquid-crystal retarder. This year we have devised a much simpler and less expensive method that can be implemented using readily available components. We have also worked out mathematical relationships useful for designing a system capable of generating an optical waveform having an arbitrary shape and amplitude.